Technical Library | 2023-05-22 17:46:29.0
Over the past several years, much research has been performed and published on the benefits of stencil nano-coatings and solvent under wipes. The process improvements are evident and well-documented in terms of higher print and end-of-line yields, in improved print volume repeatability, in extended under wipe intervals, and in photographs of the stencil's PCB-seating surface under both white and UV light. But quantifying the benefits using automated Solder Paste Inspection (SPI) methods has been elusive at best. SPI results using these process enhancements typically reveal slightly lower paste transfer efficiencies and less variation in print volumes to indicate crisper print definition. However, the improvements in volume data do not fully account for the overall improvements noted elsewhere in both research and in production.
Technical Library | 2023-04-17 17:05:47.0
In an ideal world, manufacturing devices would work all of the time, however, every company receives customer returns for a variety of reasons. If these returned parts contributed to a fail, most companies will perform failure analysis (FA) on the returned parts to determine the root cause of the failure. Failure can occur for a multitude of reasons, for example: wear out, fatigue, design issues, manufacturing flaw or defect. This information is then used to improve the overall quality of the product and prevent reoccurrence. If no defect is found, it is possible that in fact the product has no defect. On the other hand, the defect could be elusive and the FA techniques insufficient to detect said deficiency. No-clean flux residues can cause intermittent or elusive, hard to find defects. In an attempt to understand the effects of no-clean flux residues from the secondary soldering and cleaning processes, a matrix of varying process and cleaning operation was investigated. Of special interest, traveling flux residues and entrapped residues were examined, as well as localized and batch cleaning processes. Various techniques were employed to test the remaining residues in order to assess their propensity to cause a latent failure. These techniques include Surface Insulation Resistance1 (SIR) testing at 40⁰C/90% RH, 5 VDC bias along with C32 testing and Ion Exchange Chromatography (IC). These techniques facilitate the assessment of the capillary effect the tight spacing these component structures have when flux residues are present. It is expected that dendritic shorting and measurable current leakage will occur, indicating a failing SIR test. However, since the residue resides under the discrete components, there will be no visual evidence of dendritic growth or metal migration.
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